1. Field of the Invention
The invention relates to a finishing tool for precision machining of holes, comprising a chunk unit, driving head and a replaceable cutting element having at least one cutting blade, said element supported by a cylindrical supporting shaft which includes a drive pin projecting from said supporting shaft on at least one side. The supporting shaft is inserted into a cylindrical hollow of said driving head which includes a guiding recess that opens into a support groove for said drive pin.
2. Discussion of the Prior Art
Considerable demands on general precision regarding manufacturing and material quality are usually placed upon the finishing tools for precision machining of holes, considerably increasing the costs of such machining and the final prices.
The costs can be greatly reduced by providing a tool with an elongated shank for enabling flexible guidance into a pre-bored hole and compensation of possible misalignments of the hole and of the tool.
Tools with replaceable cutting elements which wear out sooner than supporting elements of the tool are well-suited for such application. Replaceability of the cutting element is economically advantageous in tools with abrasion resistant coatings, e.g. titanium nitride. Accordingly, effective design of replaceable cutting elements is particularly acute with the tools needed to finish small and medium diameter holes, or those within the range of 5 to 25 mm (0.196-0.0984 inches).
Tools with elongated shanks and with two to four carbide sintered guiding plates located around the circumference of the cutting part, together with a replaceable cutting blade chucked in the groove of the tool head using screws are also well known. However, the disadvantages of said design results with relatively lower productivity because of machining with only one blade and the high demands placed upon the tool holder, giving itself to the fact that the replacement and adjustment of the cutting blade chucked by a screw connection is relatively difficult, particularly with multi-spindle machines, thereby increasing idle time of the machines.
The disadvantages of these designs is the relatively unsafe fixation of the drive pin within the support groove. Typically, only a friction resistance against the effect of said compression spring hold the pin screws, resulting in spontaneous release and disengagement of the replaceable tool due to the inertial forces during stoppage of the tool or due to its impact transfer into the working position. Another significant disadvantage is that when reaming tools are used to ream smaller sized holes, it is impossible to make the outside diameter of the driving head smaller than the hole being reamed, precluding use of such tools to make deep holes.
The same disadvantage also appears in U.S. Pat. No. 2,057,143 where a further disadvantage includes the possibility of clogging of the drive pin seating groove with cuttings and impurities, thereby resulting in unreliable operation.
Also, lug type closures are well known but are dimensionally unsuitable for application on exchangeable reamers for a number of reaming operations, such as deep reaming and for those tools with a rear guide.